1. Field of the Invention
The present invention relates to a non-aqueous pigment ink and a pigment dispersant for a non-aqueous pigment ink.
2. Description of the Related Art
The coloring materials for inks used in inkjet recording systems can be broadly classified into materials that use pigments and materials that use dyes, and there is a growing tendency for the use of inks that use pigments as the coloring materials, as such inks exhibit the excellent levels of light resistance, weather resistance and water resistance that are required for high image quality printing.
In terms of the solvent, inks can be broadly classified into aqueous inks and non-aqueous inks. Non-aqueous inks that do not use water as the ink solvent, including solvent-based inks that use a volatile solvent as the main constituent and oil-based inks that use a non-volatile solvent as the main constituent, exhibit superior drying properties to aqueous inks, and also exhibit excellent printability.
In non-aqueous inks, a pigment dispersant that dissolves in the solvent is generally used, but because this pigment dispersant enhanced the affinity between the solvent and the pigment, when the solvent penetrates into the recording medium such as a paper, the pigment tends to be also drawn into the interior of the recording medium. As a result, the print density tends to decrease, and show-through becomes more prevalent.
One pigment dispersant that has been proposed is formed from non-aqueous resin dispersion microparticles composed of an acrylic polymer containing an alkyl (meth)acrylate unit having an alkyl group of 12 or more carbon atoms and a (meth)acrylate unit having a urethane group (see Patent Document 1). Low-viscosity inks are more suitable as inkjet inks, but when the polymer containing urethane groups from Patent Document 1 is added to an ink, the viscosity of the ink tends to increase. Accordingly, further improvements are required in terms of obtaining good pigment dispersibility without requiring the introduction of urethane groups.
[Patent Document 1] JP 2010-1452 A
An object of the present invention is to provide a non-aqueous pigment ink and a pigment dispersant for a non-aqueous pigment ink that yield high image density, reduced show-through and favorable storage stability.